Blog - Urban Forests

Urban Trees Help Clean Our Stormwater

In urban environments many cities around the globe use
biofiltration systems to capture and filter potentially contaminated water
running off and causing pollution. The research on how soils and woody plants
like trees filter water is not extensive and is lacking. The University of
Melbourne tried to fill in this gap as much as possible with specifically
designed experiment, detailed in an article by the American Society of Agronomy.

The experiment was based on four different trees commonly
used as street trees in Australia; the soils were varied while some trees were
not planted to serve as controls. They watered the trees with either a solution
similar to stormwater or regular tap water. The stormwater solution contained
high levels of nutrients such as nitrogen and phosphorus. These are typical in
areas where you have fertilizer runoff contaminating stormwater runoff. These
levels can quickly go from nutrient to contaminant and stimulate algal blooms
creating toxicity in those water bodies.
This can result in fish death, loss of biodiversity in the water and also dead
zones.

This project spanned 13 months and measured how well the
different tree species grew and took extra nutrients out of the stormwater. All
four species receiving stormwater grew significantly larger than those
receiving tap water, demonstrating all have potential to thrive under urban
conditions. The results also indicated the trees are good at unpacking
nutrients from stormwater. The unplanted soils on the other hand showed
leaching of nutrients. It appeared that the species selection was not essential
to maximize the nutrient removal performance of the biofiltration system.

Biodiversity and biofiltration is critical within our cities
and we can all contribute to this by planting our own trees to be a part of
that system. Each Tree In A
Box kit has the potential to grow multiple trees and can create your own
urban forest in your front yard, or even in potted plants on your apartment or
condominium terrace.